Direct chronopotentiometric method for ascorbic acid determination in fermented milk products

The conditions of electrochemical oxidation of ascorbic acid using glassy carbon electrode were studied leading to the development of a chronopotentiometric method that was used in the analysis of fermented milk products. The effects of the most important experimental parameters of chronopotentiometry including the type and concentration of the supporting electrolyte, initial potential and oxidation current were investigated and optimised in respect to electro-oxidation of ascorbic acid. The use of 0.15 mol/dm3 HCl as a supporting electrolyte yielded a well-defined analytical signal of ascorbic acid at ∼0.97 V (versus Ag/AgCl, KCl 3.5 mol/dm3). The linear response of transition time on ascorbic acid content was obtained in the concentration range of 0.5–80 mg/dm3 with achieved limit of detection of 0.021 mg/dm3 and limit of quantification of 0.069 mg/dm3. Defined chronopotentiometric method was applied in ascorbic acid quantification in milk products fermented with kombucha culture. The reliability of the proposed chronopotentiometric method was verified by comparison with HPLC and by recovery assays. Statistical comparison showed that there was no significant difference between the results of the proposed and HPLC methods (t = 0.4747 < t0.05 = 1.950). In the analysis of real samples, method showed to be simple (no sample pre-treatment), rapid (1–5 s), sensitive and reproducible, being suitable for routine analysis of ascorbic acid in fermented milk products. Furthermore, chronopotentiometric method allows analysis of foodstuffs under moderate price, avoiding time-consuming sample preparation steps.